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      <h2><a href="./">Go by Example 中文版</a>: Ticker</h2>
      
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            <p><a href="timers">定时器</a> 是当你想要在未来某一刻执行一次时使用的
- <em>打点器</em> 则是为你想要以固定的时间间隔重复执行而准备的。
这里是一个打点器的例子，它将定时的执行，直到我们将它停止。</p>

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            <a href="http://play.golang.org/p/tECjr_Chmrc"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>

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          <div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
    <span class="s">&quot;fmt&quot;</span>
    <span class="s">&quot;time&quot;</span>
<span class="p">)</span>
</pre></div>

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          <div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>

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            <p>打点器和定时器的机制有点相似：使用一个通道来发送数据。
这里我们使用通道内建的 <code>select</code>，等待每 500ms 到达一次的值。</p>

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          <div class="highlight"><pre>    <span class="nx">ticker</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="mi">500</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span>
    <span class="nx">done</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">bool</span><span class="p">)</span>
</pre></div>

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          <div class="highlight"><pre>    <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
        <span class="k">for</span> <span class="p">{</span>
            <span class="k">select</span> <span class="p">{</span>
            <span class="k">case</span> <span class="o">&lt;-</span><span class="nx">done</span><span class="p">:</span>
                <span class="k">return</span>
            <span class="k">case</span> <span class="nx">t</span> <span class="o">:=</span> <span class="o">&lt;-</span><span class="nx">ticker</span><span class="p">.</span><span class="nx">C</span><span class="p">:</span>
                <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Tick at&quot;</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
            <span class="p">}</span>
        <span class="p">}</span>
    <span class="p">}()</span>
</pre></div>

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            <p>打点器可以和定时器一样被停止。
打点器一旦停止，将不能再从它的通道中接收到值。
我们将在运行 1600ms 后停止这个打点器。</p>

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          <div class="highlight"><pre>    <span class="nx">time</span><span class="p">.</span><span class="nx">Sleep</span><span class="p">(</span><span class="mi">1600</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span>
    <span class="nx">ticker</span><span class="p">.</span><span class="nx">Stop</span><span class="p">()</span>
    <span class="nx">done</span> <span class="o">&lt;-</span> <span class="kc">true</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Ticker stopped&quot;</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>

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            <p>当我们运行这个程序时，打点器会在我们停止它前打点 3 次。</p>

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          <div class="highlight"><pre><span class="gp">$</span> go run tickers.go
<span class="go">Tick at 2012-09-23 11:29:56.487625 -0700 PDT</span>
<span class="go">Tick at 2012-09-23 11:29:56.988063 -0700 PDT</span>
<span class="go">Tick at 2012-09-23 11:29:57.488076 -0700 PDT</span>
<span class="go">Ticker stopped</span>
</pre></div>

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